Configuration of the Water Molecule in Cupric Fluoride Dihydrate at 298°K

The crystal structure of cupric fluoride dihydrate at 298°K has been redetermined from three-dimensional, single crystal, neutron diffraction data. Least-squares refinement of 163 independent, observed reflections gave a final, weighted R index Rw = 0.038. The H–O–H angle in the water molecule is 110.6° ± 0.2°, which, in contrast to the value 115.5° ± 0.4° found in an earlier study, is not significantly different from the tetrahedral angle of 109.5°. Thermal vibration is highly anisotropic, with much larger amplitudes perpendicular to infinite, hydrogen-bonded sheets than parallel to the sheets.